Tabs

February 22, 2011

This was among the first in the recent spate of genome-wide population structure studies, and better ones have been done since then that paint a clearer picture. Here, the sampled populations are divided into broad "northern" and "southern" clusters, and the authors conclude the following about Italians:

Conversely, Italy appears to be a zone of sharp differentiation over small distances. Some Italians cluster with the northern Europeans, whereas others fall into the southeastern grouping (fig. 4A).

Even though the text says no such thing, everyone automatically assumes that it's Northern Italians who are clustering with Northern Europeans, and that the observed pattern is representative of Italy's genetic structure. But in fact, the three individuals in question are Southern Italians, and the North-Central Italians (two Tuscans from the Coriell database) cluster even farther to the "south" than Sicilians:

Either way, the authors' conclusion is unfounded, because those few individuals are outliers that don't represent the average. In subsequent studies that have used larger sample populations and more genetic markers, all Italians cluster with other Southern Europeans according to geographical location, and are clearly distinguished from both Northern Europeans and Ashkenazi Jews. Even in a similar study from the year before, Seldin et al. (2006), there was no overlap between a sample of 86 Northern, Central and Southern Italians and various samples from farther north in Europe.

Although it is a bit surprising to find so many outliers in such a small sample, they're not unusual in and of themselves, and more often than not they're Northern and Central Europeans. In fact, in Bauchet's Figure 4A, you can see a German individual in the "southern" cluster, and different studies have shown similar outliers from Britain, France, Belgium, Scandinavia and Austria, among other places.

On a side note, it's also worth mentioning that non-Caucasoid admixture from Africa (Negroid) and Asia (Mongoloid) is as negligible in Bauchet's Italian samples as it is in the other European samples.

February 1, 2011

After centuries of speculation about why Rome fell, including stupid racial theories, could the explanation be, not human, but environmental? A new study suggests that climate instability played a central role in the collapse:

Climate variations have influenced the agricultural productivity, health risk, and conflict level of preindustrial societies. Discrimination between environmental and anthropogenic impacts on past civilizations, however, remains difficult because of the paucity of high-resolution palaeoclimatic evidence. Here, we present tree ring-based reconstructions of Central European summer precipitation and temperature variability over the past 2500 years. Recent warming is unprecedented, but modern hydroclimatic variations may have at times been exceeded in magnitude and duration. Wet and warm summers occurred during periods of Roman and medieval prosperity. Increased climate variability from ~AD 250 to 600 coincided with the demise of the Western Roman Empire and the turmoil of the Migration Period. Historical circumstances may challenge recent political and fiscal reluctance to mitigate projected climate change.

[...]

Exceptional climate variability is reconstructed for AD ~250-550, and coincides with some of the most severe challenges in Europe's political, social and economic history, the MP [Migration Period]. Distinct drying in the 3rd century paralleled a period of serious crisis in the WRE [Western Roman Empire] marked by barbarian invasion, political turmoil and economic dislocation in several provinces of Gaul, including Belgica, Germania superior and Rhaetia. Precipitation increased during the recovery of the WRE in the 300s under the dynasties of Constantine and Valentinian, while temperatures were below average. Precipitation surpassed early imperial levels during the demise of the WRE in the 5th century before dropping sharply in the first half of the 6th century. At the same time, falling lake levels in Europe and Africa accompanied hemispheric-scale cooling that has been linked with an explosive, near equatorial volcanic eruption in AD 536, followed by the first pandemic of Justinian plague that spread from the Eastern Mediterranean in AD 542/543. Rapid climate changes together with frequent epidemics had the overall capacity to disrupt the food production of agrarian societies.